Want to speak to Emma Tennant? First you have to catch her. She is about to have lunch with a publisher. She is organising a holiday in Corfu. Her answering machine directs me to a mobile. She is 70, but Tennant’s phone buzzes as frequently as any teenager’s.

Similarly, describing Tennant’s career is like stuffing an octopus into a string bag. How many books has she written? She is not sure. “I haven’t counted,” she says blithely. “When a writer is prolific, their publisher says that they’ve written over 20. I’d think I’ve done over 30, but maybe over 20 is safer.”

Her latest is a novella for teenagers, Seized, a modern reworking of Kidnapped set in Greece. Before that she produced a comic novel, The Autobiography of the Queen, in which the monarch wearies of Philip and heads off for a new life in the Caribbean. She has also written several volumes of memoirs. As the daughter of Christopher, the second Baron Glenconner, half-sister to Colin Tennant, (the third baron), aunt to models Stella Tennant and Iris Palmer and the on-off mistress of Ted Hughes, there is rich material there.

It is for Pemberley, her sequel to Pride and Prejudice, that Tennant is best known. It rode the post-Colin Firth wave of Austenmania, became a bestseller in the UK and has been translated widely. Poland was mad for Pemberley. “The eastern Europeans,” she tells me as if everyone knows this, “are very, very big on Austen.”

Tennant’s extraordinary career has been shaped by a double portion of chips on her shoulder. Despite her impeccable connections, none of the family’s money came her way and she has always had to earn a living. It’s not the working she resents, but the assumption that she doesn’t really have to. Then there is her lack of formal education. Tennant was miserable at St Paul’s Girls’ School in London and left before her 16th birthday.

She moved among the demi-monde of 1950s and 1960s London, working as a travel writer for Queen magazine and then as an editor at Vogue. The parties were great but she struggled to find her literary voice. “I felt really crushed by intellectuals, having left school so early, and I tried to write the English social novel and they went under my bed. They vanished, I couldn’t even show them to anyone.”

It took a few home truths from a group of science fiction authors including JG Ballard and Michael Moorcock to show Tennant you didn’t need to be Margaret Drabble or Doris Lessing to get into print. “They said to me, come on, you can perfectly well do this. This is how: you have four sections of 40 pages each. Introduction of the characters is one, development of characters and their situation is two, crisis begins, three, and then the climax.”

It had not occurred to Tennant that it could be so straightforward. “I thought, it can’t be as simple as that. And then I realised, with some things, it could be.”

She was off, writing sci-fi comedies before moving the “imaginative elements” of the genre into more literary novels, such as The Bad Sister and Wild Nights. “It was a progression of imagination,” she says.

There is a restlessness in Tennant that sends her shooting off in these wildly different directions. It was a search for powerful characters that found her rereading the classics and wondering: what next? “How many famous characters are there, really?” she asks. “Apart from maybe Lucky Jim, who probably isn’t known by anyone under 40 anyway, who are they? That’s the most compelling thing.”

So, as well as dissecting Elizabeth and Darcy’s first year together in Pemberley, Tennant also took their story forward 20 years in An Unequal Marriage. Then there is Heathcliff’s Tale and Thornfield Hall (the story of Adele, Mr Rochester’s French ward in Jane Eyre). The sequels are playful and knowing — Pemberley begins: “It is a truth universally acknowledged, that a married man in possession of a good fortune must be in want of a son and heir — although Tennant describes them as “more of a ventriloquism, really”.

That does them down. Tennant pulls off a clever balancing act, keeping to the much-loved voice of the original while addressing questions that would never have occurred to Austen or Charlotte Bronte. “The mores have changed,” she says. “Then, marriage was the end and happy ever after. Now we want to know: what would this marriage actually have been like, having to run this huge great house while being sneered at by Lady Catherine de Bourgh.”

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